Study On The Conservation Biology Of Magnolia Championii Benth

Magnolia championii Benth, belonging to Magnoliaceae Jussieu genus Magnolia Linn subgenus Magnolia Dandy section Gwillimia DC., is distributed in south-east and south-west of Guangdong, south of Guangxi and Guizhou. Its population numbers and sizes in nature degenerate gradually and the population reproduction mode presents the decaying trend. The plants are difficult to be found in the area where the specimen was collected in the past time. M. championii is protected by the Forestry Regulations in Hongkong. This dissertation investigated the reproductive biology and endangered mechanism of the vulnerable plant based on the study of embryogenesis, floral character, pollination biology, seed physiology. The main results are as follow.1. The result of field exploring and specimen consulting indicated that the over-exploitation on the forest had destroyed the habitat of M. championii. For better water circumstance, the plant immigrated from the top of mountain to the valley at low altitude, where the shading surrounding declined its ability of reproduction and growth, as well as the chance of seed spread by birds. The low reproduction ability result in the lack of seedlings and the trend of being replaced by other dominance plants on population.2. The results of developmental anatomy of embryo present that the much abnormal phenomenon at every stage of the embryogenesis is the main reason of low seed set rate. There are different abortion ratio of secondary sporogenous cell, microspore mother cell, tetrads and mononucleus microspore during the formation of microspores and development of male gametes. The worst abortion is that all of the mononucleus microspore stop developing because of the absence of nutriment which should be transfered from the connection to anther wall orderly. The main abnormal development was observed that the functional megaspores increased its volume and divided one or two times, then stop developing at the stage of monosporic, bisporic and tetrasporic embryo sac, which finally come to an empty sac. In addition, the abortion of lots of synergid in mature embryo sacs could also be seen. Based on the seeding rate by means of artificial pollination, the fertile embryo sac rate is 8.95%. The more important reason for the failure to reproductive is the abnormal development of embryogenesis.